Spectacle lens types include not only mono-focal lenses, but also progressive power lenses.
Examples of conventional progressive power lenses includes a spectacle lens which has a corridor where the radius of curvature progressively changes along the principal meridian passing through approximately the center of the lens, so that a predetermined addition power is provided between the center of the distance portion and the center of the near portion on the principal meridian (see PTL 1).
In the progressive power lens according to PTL 1: a fitting point is set between the start point and the end point of the corridor; the average gradient of the addition power from the start-point of the corridor to the vicinity of the fitting point differs from the average gradient of the addition power from the vicinity of the fitting point to the end point of the corridor; and about 0.5 diopters of power is added to the distance power at the fitting point.
In prior art according to PTL 1, about 0.5 diopters of power is added to the distance power at the fitting point as the target addition power, regardless the addition power prescribed for each user (prescription addition power), hence a region about 2 m ahead, which is set as the target distance, can be clearly viewed, regardless the prescription addition power of the user.